A case study and damage assessment of some heavy section components operating for more than 100 000 h in fossil-fired power plants

Abstract

A main steam pipe T-piece, a main steam stop valve and a reheater steam piping Y-piece have been taken out of three different power boiler plants that have seen each an accumulated service life of over 100 000 h, involving more than 500 start-and-stop operations, and their states of degradation examined. The degradation was assessed in terms of the changes found in the mechanical properties and the metallographic structure, the flaws actually detected in them, and analyses of the distributions of temperature and stress for start-and-stop operations as well as steady state were calculated on the basis of the service histories. Detailed stress analysis afforded information to indicate the portions that sustained large damage, and on which damage assessment calculations were conducted. The remaining service lifetime calculation was conducted on the basis of analyses of propagation of the defects and showed that the component had sufficient allowances for continued service under severe operating conditions.